#编写一段程序，对给定
word = input('请输入一串英文字符串:')
word = word.lower()  #将字符串全部转换为小写
word_dict = {}
for i in word:
    if i.isalpha():
        if i in word_dict:
            word_dict[i] +=1
        else:
            word_dict[i] = 1
word_dict = sorted(word_dict.items(), key=lambda x:x[1],reverse=True)
for i in word_dict:
    print(i)
